Structural and optical studies of dielectric and metallic organic films

We report on x-ray structural and optical measurements on two types of organic materials: Polypyrrole (PPY) free-standing films produced by electrodeposition, and doped with p-toluenesulfonate, which exhibit metallic character; and thin films of para-Hexaphenyl (PHP) (an oligomer of poly(para-phenylene) which has been successfully used in blue light emitting diodes) produced by molecular beam deposition on glass substrates showing dielectric, semiconducting character. X-ray diffraction measurements reveal that both film types show a well ordered structure leading to anisotropy, but with a different chain orientation governed by the film growth mechanism. The PHP films grow with chains oriented near-normal to the substrate surface, while the chains in PPY films lie predominantly in the film plane. Refractive indices and absorption coefficients, calculated from optical reflectance and transmission spectra, exhibit a pronounced microstructure dependence, where the refractive indices of PPY in the infra-red region were strongly influenced by the doping methods.